docs: def surface_nodes(self):
          """
          :param points: a list of Point objects
          :returns: a Node of kind 'griddedSurface'
          """
          line = []
          for point in self.mesh:
              line.append(point.longitude)
              line.append(point.latitude)
              line.append(point.depth)
          return [Node('griddedSurface', nodes=[Node('gml:posList', {}, line)])]